What information should be considered personal knowledge?

http://arstechnica.com/tech-policy/2014/10/virginia-judge-police-can-demand-a-suspect-unlock-a-phone-with-a-fingerprint/

The new court ruling in VA allows police to force you to hand-over you fingerprint to unlock your phone. This ruling draws a line between testimony and personal data. Before the age of texting and phone calls most conversations between people were held in private, while today every digital conversation we have is recorded in and data mined. In a court case you would not be required to divulge what was said in the conversation, but now all the police need is the decryption key in order to obtain what was said. Today our devices have become a place for a vast majority of our personal information to be stored. Should  the data on your cell phone count as personal knowledge or should be available for police to use against you in court?

Depends on case. That is sort of general (non specific) questionn you asked.

If for example, you recieved treat in format of text, that data must be availalbe to hte court, and it is in your interest to be that way.

On the other hand, if "you done" such thing, your data should be confiscated and checked in order to look at validity of accusations.

For example, from my personal experience, once, police confiscated my number and re-checked accusations. They found them to be valid or invalid, and returned device.

In short, if that data is relevant to the case (textual msg, call lists etc.), it should be (and it is) available for police and usage in court. Ofc, with warrant, that is by default. Without warrant, it should be unavailable.